1. Field of the Invention
The present invention relates to a high average power magnetic modulator for metal vapor lasers.
2. Description of Related Art
Extensive experience with thyratron driven capacitor inversion circuits for driving moderate power copper lasers (.apprxeq.10 kW input) leads to the conclusion that this type of circuit would not exhibit the lifetime required for the new higher power copper vapor lasers. The dI/dt, peak amplitudes, and repetition rates of existing modulators caused premature thyratron failure due to cathode depletion and anode erosion; a factor of three increase in power requirements would only increase the problem. An examination of other types of modulator switches, technologies, and circuit topologies has not revealed a simple, inexpensive, or proven alternative. It was determined that more complex magnetic compression circuits could reduce the electrical stress on the thyratron thereby potentially increasing lifetime; but their use, in turn, raised questions concerning jitter, long term reliability, efficiency, and component lifetimes.
Magnetic compression circuits are well-known in the art for having the capability of compressing a first series of voltage pulses, each having a first duration to form a second series of voltage pulses, each having a shorter second duration ("pulse width"). The first series of voltage pulses are typically generated by a thyratron circuit. The second series of voltage pulses can be used for application to a laser, such as a metal vapor laser, to affect generation of a corresponding series of laser beam pulses. Such pulsed lasers are utilized in many applications such as medical diagnostics, laser isotope separation of an atomic vapor (known as an AVLIS (Atomic Vapor Laser Isotope Separation) process), and many other applications. It is frequently desirable to increase the amplitude of the voltage of the pulses prior to application to the laser.
A magnetic compression circuit generally utilizes a multi-stage LC network to provide the compression. Such magnetic compression circuits usually include a switching means at the last stage comprising a single turn. The total energy being put through such a device determines the minimum amount of magnetic core material which is required for the application. Additional core material above this minimum amount reduces efficiency and leads to additional losses. Thus it is preferable to build a core having as close to the minimum required amount of core material as is possible. A multi-turn output switch is desirable in order to obtain a higher packing factor and reduce the overall volume of the device. However, traditional methods of shielding a multi-turn output switch (e.g., winding wire about a torroid) serve to unnecessarily increase the volume of magnetic material required, resulting in less electrical efficiency. In accordance with the present invention a multi-turn output switch is provided which permits a high packing factor without increasing the amount of core material required.